Optimizing Proton Conductivity in Sulfonated Polystyrene Membranes via Phosphorous Pentoxide Doping

Recently, Proton conducting membrane fuel cells (PCMFCs) have been recognized as a potential future and excellent medium for efficient power sources. In this present work, Polystyrene has been used to make a proton conductive membrane, mixing with phosphorus pentoxide (P2O5), targeting to achieve low cost and high proton conductivity under low humidity conditions. Several membranes are studied with varying amounts (three compositions: 5 wt.%, 10 wt.%, and 20 wt.%) of P2O5 concerning polystyrene weight and doped in 20% diluted sulfuric acid. It is expected that a new proton transport pathway is provided between the phosphoric acid and sulfuric acid in dry conditions. Results of conductivity, obtained by Electrochemical Impedance Spectroscopy (EIS), have shown excellent proton conductivity at room temperature. The 10 wt.% modified P2O5 membrane exhibited a higher order of proton conductivity, approximately two orders of magnitude compared to pure PS membrane at dry conditions (approximately 10-2 S/cm), which is the highest value among the fabricated membranes. The Fourier transform infrared spectrometer (FTIR) analysis confirmed the sulfonation of the modified membranes. These membranes are also characterized by scanning electron microscopy (SEM) and tensile test. The tensile test showed the highest strength of 1.8 MPa; while the SEM images proved the porous structure of the membranes, which is helpful to improve the proton conducting membrane (PCM) structure. So, the 10 wt.% P2O5 modified membrane Is a promising candidate as a novel PCM and have potential applications for use in fuel cells.